Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
  • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
  • C09C1/28—Compounds of silicon
  • C09C1/30—Silicic acid
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/113—Silicon oxides; Hydrates thereof
  • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
  • C01B33/18—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof
  • C01B33/187—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof by acidic treatment of silicates
  • C01B33/193—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof by acidic treatment of silicates of aqueous solutions of silicates
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/34—Silicon-containing compounds
  • C08K3/36—Silica
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
  • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/12—Surface area
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/80—Compositional purity
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/90—Other properties not specified above

Definitions

• the present invention relates to novel precipitated silica particulates, and, more especially, to certain hydrophilic precipitated silica particulates well adapted for use as a reinforcing filler for the curable organopolysiloxanes and for other elastomers.
• a major object of the present invention is the provision of improved precipitated silica particulates, far better adapted as filler materials for the reinforcement of organosilicic polymers and other elastomers, which silica particulates are characterized as comprising the following combination of properties:
• the improved precipitated silica particulates preferably display the following properties:
• the BET specific surface area is determined by the Brunauer, Emmet & Teller method described in Journal of the American Chemical Society, volume 60, page 309 (1938).
• CTAB surface area is determined by absorption of cetyl-trimethylammonium bromide with a pH of 9, using the Jay, Janzen & Kraus method [Rubber Chemistry and Technology, 44, pages 1287-1296 (1971)].
• silica 3 g are charged into a mold or die having an internal diameter of 25 mm and a height of 80 mm, and then a piston is positioned thereabove. A given weight is added to the piston such as to exert a pressure of 4 kg/cm 2 upon the silica. The specific volume of the silica is then measured. This is the volume "V o " expressed in cm 3 /g (initial volume).
• the V 600 is determined in the same manner, but by exerting a pressure of 600 kg/cm 2 .
• drying is effected at a temperature of 190° C. for 11/2 hours, before making the measurement.
• the residual sodium content reflects the total remaining amount of sodium.
• the residual sodium content is measured by flame spectroemission after dissolving the silica in hydrofluoric acid.
• the pH is measured on a 5% silica suspension in water.
• organosilicic compositions according to the invention which, after vulcanization, are reinforced by the subject silica particulates, is not critical.
• organopolysiloxane compositions are either solid, gummy, pasty or liquid.
• the vulcanizable organosilicic polymer reinforced is such that, with R denoting the hydrocarbon radicals thereof, which are linked to the silicon atoms, the ratio between the total number of radicals R and the total number of silicon atoms is between 0.5 and 3.
• the other available valencies of silicon are bonded to heteroatoms such as oxygen or nitrogen, or else to polyvalent hydrocarbon radicals.
• the filled organosilicic compositions according to the invention are organopolysiloxane compositions in which the organopolysiloxane may be either straight or branched chain, or cross-linked, and may possibly comprise, in addition, hydrocarbon radicals bearing reactive groups or functions, such as, for example, hydroxyl groups, hydrolyzable groups, alkenyl groups, hydrogen atoms, and the like.
• organopolysiloxanes which constitute the main ingredients of the compositions according to the invention comprise siloxane recurring units having the following structural formula: ##EQU1## possibly also comprising those siloxane units having the following structural formula: ##EQU2##
• R represents a group of hydrocarbon nature, which is not hydrolyzable, and which radical may be:
• aryl, alkylaryl and haloaryl radicals having from 6 to 8 carbon atoms and containing from 1 to 4 chlorine and/or fluorine atoms, and
• Z is a hydrogen atom, an alkenyl group, a hydroxyl group, a hydrolyzable atom or a hydrolyzable group
• n is an integer of 0, 1, 2 or 3;
• x is an integer of 0, 1, 2 or 3;
• y is an integer less than or equal to 2.
• the following are exemplary of the organic radicals R which are directly linked to the silicon atoms: the groups methyl; ethyl; propyl; isopropyl; butyl; isobutyl; ⁇ -pentyl; t-butyl; chloromethyl; dichloromethyl; ⁇ -chloroethyl; ⁇ , ⁇ -dichloroethyl; fluoromethyl; difluoromethyl; ⁇ , ⁇ -difluoroethyl; 3,3,3-trifluoropropyl; trifluorocyclopropyl; 4,4,4-trifluorobutyl; 3,3,4,4,5,5-heptafluoropentyl; ⁇ -cyanoethyl; ⁇ -cyanopropyl; phenyl; p-chlorophenyl; m-chlorophenyl; 3,5-dichlorophenyl; trichlorophenyl; tetrachlorophen
• the organic radicals which are linked to the silicon atoms are methyl, phenyl or vinyl radicals, which radicals may possibly be halogenated or may be cyanoalkyl radicals.
• the sumbols Z may be hydrogen atoms, chlorine atoms, vinyl groups, hydroxyl groups or hydrolyzable groups such as amino, amido, aminoxy, oxime, alkoxy, alkoxyalkoxy, alkenyloxy, acyloxy, and the like.
• organopolysiloxane and, therefore, the ratios between the siloxane units (I) and (II) and the distribution thereof is, as is known, selected in dependence on the use envisaged and in dependence on the vulcanization treatment which ultimately is to be performed on the composition.
• compositions may be those which are vulcanizable at elevated temperature under the action of organic peroxides, such as 2,4-dichlorobenzoyl peroxide, benzoyl peroxide, t-butyl perbenzoate, cumyl peroxide, di-t-butyl peroxide, and the like.
• organic peroxides such as 2,4-dichlorobenzoyl peroxide, benzoyl peroxide, t-butyl perbenzoate, cumyl peroxide, di-t-butyl peroxide, and the like.
• the organopolysiloxane comprising such compositions then essentially consists of the siloxane units I and does not contain any hydrolyzable atoms or groups.
• polymethylpolysiloxanes which are terminated by trimethylsilyl groups represent a particularly important example of this particular category from an industrial point of view.
• Vulcanization can also be effected at ambient temperature or at moderate temperature by effecting cross-linking between vinylsilylated or hydrogenosilylated groups, the hydrosilylation reaction being conducted in the presence of catalysts such as derivatives of platinum; the organopolysiloxanes employed do not then contain hydrolyzable groups or atoms.
• Vulcanization can also be effected under the action of moisture.
• the organopolysiloxanes contained in the compositions of this type contain hydrolyzable groups or atoms as defined above.
• the siloxane units II containing such groups represent at most 15% by weight of the total mass of the organopolysiloxane used.
• the organopolysiloxane compositions of this type generally contain catalysts such as tin salts.
• the organopolysiloxanes employed in these compositions are typically straight-chain, branched or cross-linked polysiloxanes comprised of the units I and II wherein Z is a hydroxyl group and x is at least equal to 1.
• the cross-linking agent may be a polyfunctional silane, such as methyltriacetoxysilane, isopropyltriacetoxysilane, vinyltriacetoxysilane, methyltris(diethylaminoxy)silane, or the like.
• Various other compounds such as silicates may also be used as cross-linking agents.
• the precipitated silica particulates according to the invention are generally non-microporous, have a large surface area, and have a high level of particle finenes.
• the silica particulates according to the invention can be prepared in a number of ways utilizing known techniques, e.g., initial addition of all the silicate, the simultaneous addition of silicate and acid, post-addition treatments, etc., on condition that the values of the various interdependent parameters are properly selected or predetermined such as to give rise to the desired results, with variation in one of the parameters being compensated for by the selected values of the other parameters.
• aqueous alkali metal silicate solution carbon dioxide or an aqueous solution of a strong mineral acid
• the addition of the acid solution is generally effected in a plurality of phases and preferably the addition of acid is interrupted as soon as the opalescence which indicates a rapid rise in viscosity occurs, the addition of acid being resumed only after the gel breaks, such as to adjust the pH-value to from 9 to 7.
• the temperature is rapidly raised and is maintained close to 100° C. for at least 20 minutes and preferably for 30 minutes.
• the washing operation is preferably successively performed by means of pure water which is slightly acidified to a pH-value of 5-4, and then by pure water.
• the silica is dried and micronized using the normal methods. Drying is effected, for example, in vortex current apparatus as described in published French patent application No. 2,257,326, and the dwell time therein is less than a minute.
• Micronization is performed by means of apparatus of the type Jet-O-Mizer and others, as described in Chemical Engineers Handbook of J. H. Perry, 5th edition, part 8/43.
• the conditions for the drying operation and the micronization operation are so adapted as to achieve, and in accordance with the normal methods used by one skilled in this art, suitable values as regards the parameters V o , moisture content, etc.
• the aqueous solutions of silicates contain from 50 to 120 g/l in equivalent by weight of silicon dioxide, the molar ratio SiO 2 /alkaline oxide (Na 2 O . . . ) is from 2.5 to 4 and the acid solutions can be used in diluted or concentrated form.
• the aqueous silicate solution neutralization temperature is initially between 50° C. and 95° C. before the subsequent heating operation for blocking the micropores.
• the neutralization temperature must be selected at a higher value in proportion to increasing dilution of the medium in which the gel and then the silica precipitate will be formed. With the same degree of dilution, the rise in temperature makes it possible in fact to reduce the surface area of the precipitated silicas; if the medium is more concentrated, operation will then be in lower temperature regions (50° to 70° C., for example).
• a sequestering agent to the aqueous silicate solution, thereby making it possible, at least partially and preferably totally, to complex the traces of metallic impurities (in particular, the alkaline earth metals such as calcium and magnesium) which in practice are always present in the silicate, in very small amounts.
• metallic impurities in particular, the alkaline earth metals such as calcium and magnesium
• complexing agents which are suitable: ethylenediamine tetracetic acid (EDTA), sodium nitrilotriacetate (NTA), sodium diethylenetriaminopentacetate (DTPA) and sodium tripolyphosphate (STPP).
• aqueous alkaline silicate solution in a reaction vessel of small capacity (with respect to the total amount of aqueous silicate solution), by regularly circulating therein and in a closed circuit configuration, the aqueous sodium silicate solution which is initially introduced into a container of substantial size; after neutralization, the mixture is returned to the container.
• neutralization with recirculation comprises using acid to neutralize the aqueous alkaline silicate solution in a reaction vessel of small capacity (with respect to the total amount of aqueous silicate solution), by regularly circulating therein and in a closed circuit configuration, the aqueous sodium silicate solution which is initially introduced into a container of substantial size; after neutralization, the mixture is returned to the container.
• the precipitated silica particulates according to the invention can be prepared by using a process similar to that described immediately above, but in which, after the pH-value of the medium has been adjusted to a value of from 9 to 7 by a flow of acid, a treatment referred to as "post-addition" is performed, while maintaining approximately the same temperature conditions, such treatment consisting of adding an aqueous silicate solution providing approximately 15 to 50 parts by weight of silicate per 100 parts of silicates used at the beginning of the process.
• the post-addition operation can be effected instantaneously continuously, and possibly in several operations, but it is necessary in all cases to maintain the pH-value at from 9 to 7, by an additional flow of acid.
• re-circulation similar to that described above can be employed.
• the flow of acid is continued so as to adjust the pH-value to from 5.5 to 3.5.
• the temperature of the medium is raised to a value of about 100° C.
• the silica is then separated, filtered, washed, dried and micronized as in the previous process.
• recirculation is effected in accordance with a technique similar to that described in French Pat. No. 1,160,762.
• the addition of water after breaking of the polysilicic acid gel and/or the initial addition of sequestering agent may be used.
• the silica particulates by simultaneous addition of acid solution and alkali metal silicate solution.
• the simultaneous feedstreams are generally started on a base of dilute silicate having a pH-value of from 10.2 to 8.
• a sequestering agent is introduced into the aqueous silicate solution forming the base; the base generally represents from 15 to 20% of the final total volume.
• the acid and the silicate are introduced into the reaction vessel at a temperature of from 80° C. to 95° C., with the pH-value being maintained at from 9.8 to 10.2.
• a thermal peptization treatment is effected, with the pH-value being adjusted to from 9 to 7 and with the medium being heated to around 100° C.
• this treatment is concluded (it generally lasts at least 20 minutes), the addition of acid is resumed to adjust the pH-value to from 5.5 and 3.5.
• the silica is then separated, washed, and dried and micronized as in the preceding processes.
• it is possible to use the method of neutralization with recirculation of the silicate base in the neutralization reaction vessel this method also being similar to that described in French Pat. No. 1,160,762).
• the organosilicic compositions may contain, as a reinforcing agent, precipitated silica particulates as defined above, which have subsequently been subjected to normal post-treatment for modifying their surface properties, notably for rendering same hydrophobic.
• modified silica particulates are equally suitable for reinforcing organopolysiloxane elastomers.
• the nature of the various agents for modifying the surface properties is not critical.
• the agents used are typically organosilicic in nature, such as siloxanes (hexamethyldisilazane, etc.), alkyl silanes (trimethylsilane, etc.), alkylalkoxysilanes (trimethylethoxysilane, etc.), alkylchlorosilanes, alkenylchlorosilanes, dihydroxylorganopolysiloxanes, cyclosiloxanes, and the like, and are, for example, described in French Pat. Nos. 2,356,596 and 2,395,952.
• the precipitated silica particulates may also be heated to a temperature typically ranging from 200° to 800° C. Thus, the content in relative humidity and rehumidification is reduced.
• the silica particulates used in accordance with the present invention may have a relative moisture content which is variable depending on the production and/or storage conditions.
• the relative moisture content is generally between 2 and 6% (measured by heating for 2 hours at a temperature of 105° C.).
• the water content of the silica particulates which are incorporated in the organopolysiloxane compositions evidently depends on the intended end use. For extrudable compositions, the water content must be less than 3%.
• organosilicic compositions according to the invention contain from 5 to 50% and preferably from 10 to 40% of precipitated silica particulates which are possibly treated as defined hereinbefore.
• the compositions may contain normal fillers such as powdered quartz, diatomaceous earth, talcum, carbon black, and the like.
• the compositions may also contain various normal additives such as anti-structure agents, thermal stabilizing agents, thixotropic agents, pigments, corrosion inhibitors, and the like.
• the anti-structure agents which are also known by the name of plasticizers are generally organosilicic in nature and are introduced in a proportion of from 0 to 20 parts per 100 parts of the organosilicic composition to be reinforced. They make it possible to avoid hardening of the compositions during storage.
• the anti-structure agents may include silanes with hydrolyzable groups, or hydroxylated or alkoxylated diorganopolysiloxane oils of low molecular weight. Such compositions are, for example, described in French Pat. No. 1,111,969.
• thermal stabilizing agents which are well known to one skilled in this art, mention is made of the salts, oxides and hydroxides of iron, cerium or manganese. These additives which may be used either alone or in admixture are generally introduced in a proportion of 0.01 to 5% with respect to the weight of the organopolysiloxane.
• the organopolysiloxane compositions are prepared by simple mixing of the various ingredients of the composition, as described hereinbefore. Mixing can be carried out at ambient temperature or at elevated temperatures, and whether or not the composition comprises silica particulates which either have or have not been treated for modification of the surface properties thereof.
• the organopolysiloxane compositions according to the invention After vulcanization, the organopolysiloxane compositions according to the invention give rise to elastomers, the mechanical and thermal properties of which are on the same order as those of organopolysiloxane elastomers which are reinforced with pyrogenic silica particulates.
• the use of the organosilicic compositions according to the invention is also one aspect of the present invention, for the production of hardened materials.
• the silica particulates according to the invention can also be used for reinforcing such other elastomer materials as SBR rubbers, and the like.
• the precipitated silica used in this example was prepared in the following manner:
• the flow of acidic aqueous solution was interrupted after 10 minutes when marked opalescence had occurred; 62 liters of water were then added over a period of 15 minutes, with the temperature being maintained, and then the temperature was raised to about 90° C. after the 70th minute. This temperature was reached at the 88th minute. From that moment, 37 kg of an aqueous sodium silicate solution were added to the pre-reaction vessel, up to the 128th minute, at a rate of 625 cm 3 /minute, while maintaining the pH-value at 7.5 ⁇ 0.1 by adding the acid solution at a rate of 63 cm 3 /minute and while maintaining the temperature at from 85° C. to 90° C.
• silicate being terminated at the 128th minute, the addition of acid was continued until the pH-value was adjusted to 3.5, while continuing heating at from 90° to 100° C.
• the silica was then filtered, washed, dried by flash drying in an apparatus of the type described in French Pat. No. 2,257,326, and micronized in an apparatus of the type Jet-O-Mizer and others, as described in Chemical Engineers Handbook, 5th edition, 8-43 or 8-44.
• This silica was first used for reinforcing organopolysiloxane materials (EVC).
• the organopolysiloxane composition the vulcanization or curing agent which comprised one part of a paste containing 50% of 2,4-dichlorobenzoyl peroxide, in a polyorganosiloxane oil.
• Vulcanization or curing was then performed by heating the mixtures which were placed in molds 2 mm in thickness, for a period of 8 minutes, at a temperature of 115° C., under press force (pressure of 60 kg/cm 2 ). Th elastomers were optionally subjected to an annealing treatment for a period of 16 hours at 200° C.
• organopolyxiloane compositions to which had not yet been added a vulcanization agent were produced either at ambient temperature or at 150° C.
• the mechanical properties of the organopolysiloxane elastomers produced after vulcanization and optional annealing were compared to those of elastomers produced by replacing the precipitated silica with a pyrogenic silica having substantially the same surface area (Cab-O-Sil); BET surface area 217 m 2 /g; CTAB surface area 206 m 2 /g).
• the subject silica was next used without micronization for reinforcing other elastomers.
• the V 600 of the silica was determined to be equal to 1.23 and, when preliminarily dried at 190° C., to be 1.49.
• CM maximum torque
• CM-Cm related to the degree of cross-linking
• Induction Period time required to initiate cross-linking at the temperature of the test
• This apparatus is for subjecting a vulcanizate to alternating deformation stresses and to determine its fatigue strength.
• DCO dynamic compression at the beginning of the test.
• DCF dynamic compression at completion of the test.
• ⁇ DC DCF-DCO evoluation of the dynamic compression, related to fatigue strength.
• the percentage of dispersion is the percentage of silica dispersed in conglomerates of less than 8 microns.
• the dispersion improves in proportion to the increase in such percentage.
• the resulting slurry of precipitated silica was filtered and then washed in order to reduce the Na content to the desired level of less than 500 ppm.
• a portion of the slurry was flash dried with a device using a shaft spinning flow (Leaflash system of RHONE-POULENC), according to French Pat. No. 2,257,326 with the remainder of the slurry being dried in an oven with a gas temperature at the inlet of 500° C. and at the outlet of 150° C., partially dried at 120° C. during 15 hours.
• Leaflash system of RHONE-POULENC Leaflash system of RHONE-POULENC
• the silicate addition was terminated at the 100th minute, and the addition of acid was continued until the pH-value was 8, and then heating was effected at a temperature of 95° C. for 20 minutes. The addition of acid was then resumed to adjust the pH value to 3.5. The silica was then filtered, washed, dried, crushed and micronized, as in Example 1.
• An organopolysiloxane composition was prepared by replacing, in the recipe for the organopolysiloxane composition of Example 3, the instant precipitated silica for that of said example.
• the vulcanization conditions were identical to those of Example 1.
• An organopolysiloxane composition which was heat curable was prepared, in accordance with Example 1, by replacing the precipitated silica of that example by a precipitated silica which had been treated with octamethylcyclotetrasiloxane, and having the following characteristics:
• This particular precipitated silica was produced by heating, with octamethylcyclotetrasiloxane, the precipitated silica of hydrophilic nature, as described in Example 1.
• composition produced was then vulcanized and annealed using the mode of operation of Example 1.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Silicon Compounds (AREA)
• Pigments, Carbon Blacks, Or Wood Stains (AREA)
• Tires In General (AREA)

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Cited By (33)

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• 1979
  • 1979-12-20 FR FR7931217A patent/FR2471947A1/fr active Granted
• 1980
  • 1980-12-08 EP EP80401750A patent/EP0031271B1/fr not_active Expired
  • 1980-12-08 DE DE8080401750T patent/DE3070630D1/de not_active Expired
  • 1980-12-18 JP JP17963280A patent/JPS5696718A/ja active Granted
  • 1980-12-19 BR BR8008344A patent/BR8008344A/pt unknown
  • 1980-12-19 ES ES497951A patent/ES497951A0/es active Granted
  • 1980-12-19 CA CA367,277A patent/CA1132774A/fr not_active Expired
• 1984
  • 1984-11-20 US US06/673,269 patent/US4704425A/en not_active Expired - Fee Related
• 1989
  • 1989-08-09 JP JP1206587A patent/JPH02110144A/ja active Pending

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